Spark plug



Oct. 28, 1941. PETERS 2,260,399

SPARK PLUG.

Filed April 19, 1940 VENTOR I IN NELWLLE E PETERS 7 BY HENRY K. KING MawPatented Oct. 28, 1941 UNITED STATES PATENT OFFICE Application April 19,1940, Serial No. 330,5d6

10 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) This invention relates to animproved spark plug, and specifically to a spark plug having a causepre-ignition and without the electrical re-' 10 sistance becoming lowenough to cause a shorting of the plug to ground. Reliable firing and---long life is reasonably assured if a low temperature of the spark plugcan be maintained.

It is anobject of this invention to provide a 15 spark plug utilizingthe series gap principle and so constructed as to permit its use inmodern high output engines.

It is a further object of this invention to provide a spark plug soconstructed'that the tem- 20 perature over all portions of the plug willbe maintained at'a low temperature under severe operating conditions.

It is a still further object of this invention to provide a constructionwhich will permit the use 2 of smaller diameter plugs with a consequentincrease in thermal eiliciency, but with no loss in mechanicalruggedness and strength.

It is well known that in a laminated mica core Fig. 3 is a view similarto Fig. 1, showing second embodiment of the invention; and

Fig. 4 is an enlarged view of a fragment of Fig. 3, showing the detailsof the lower end of the plug.

Referring now to the embodiment shown in Fig. 1, the plug is built uparound the central spindle shank I, extending longitudinally thereof. Amica cigarette 2 surrounds the spindle shank throughout its length andprotrudes for a certain distance below its lower end. A metal shell 3contains the spark plug assembly. The upper portion of this shell isthin walled and spaced top of the shell. This space may be filled with apile of mica washers, the upper end 8 of the shell 3 being spun over tomaintain them in place. The space between the inner cigarette 2 and theouter cigarette 6 is filled with a pile of mica washers 2|, the upperend of the spindle shank I being flanged outwardly at 9. The micawashers 1 may be omitted, if desired. The thickened porconstruction theinterspersing of metal washers 39. tion 4 of the shell is screw threadedto fit the between the mica washers provides an increased thermalconduction from the surface of the core in contact with the flames tothe center shank which carries the heat away, but in such constandardthreaded hole in the engine cylinder.

The lower end of the shell is partially closed by a member Ill having ahole extending through its center. Between the lower end of the spindlestruction care has always been taken to prevent '88} shank I and themember I0 is located an aselectrical flashover, due to the use of themetal washers, and the regular spark gap was provided elsewhere. of gapsbetween pins, rings, or other intermediate characteristics. However,such devices are subject tolocal overheating and cause pre-ignition inhigh output engines. The device of this inven- 'tion successfullycombines the advantages of both types and eliminates some of theelectrical disadvantages of the parallel gap type while eliminating thethermal disadvantages of the series p yp Referring now to the drawing:

Fig. 1 is a cross-sectional view of one embodi- 0 and the cigarette 8.Into this space an insulating ment of the improved spark plug of thisinven-' tion, taken along its longitudinal axis.

Fig. 2 is an enlarged view of a fragment of Fig. 1, showing the detailsof the lower end of the spark plug.

It is also well known that a series v metal washers I2. "metallic paths,gives certain desirable electrical- 9. central hole through each of themica. washers sembly of washers forming a series of spark gaps. Theassembly consists of a series of mica washers I I, between which areinterspersed a series of It will be noted that the is of a largerdiameter than that through the metal washers, thus providing a series ofair gaps bridging the distance between the lower end of the spindleshank and the member I0, across 45 each of which sparking will occur.

The mica washers fit snugly against the cigarette 6. However, the outerdiameter of the metal washers is small enough that a considerableannular gap is left between each metal washer compound I3 is placed. Thelower outer corner of each metal washer is rounded at I4 to increase thedistance between this portion ofthe washer and the upper corner of theadjacent at this edge, thus preventing the occurrence of any sparking atthis point. The upper outer corner of each metal washer is smoothed oiland siightly rounded, so that the upper surface of v the washer is flatso as to provide the maximum amount of bearing surface for thesuperimposed mica washer, thus preventing breakage of the mica washer.

In the second embodiment of the invention shown in Figs. 3 and 4, thecentral spindle shank I extends below the lower end of the shell andterminates at its lower end with a strong outwardly turned flange l5.The upper portion of the plug assembly is constructed in the same manneras previously described. The lower porfiguration found in the outerportions of the metal washers of the previous embodiment is here foundin the inner portions of the washers. The outer diameter of the metalwashers in this embodiment is larger than that of the corresponding micawashers. The mica washers fit snugly against the inner cigarette 2,whereas the central hole. through each of the metal washers is largeenough to leave a central annular space between the cigarette and themetal washer, which space is filled with insulating compound l3, as inthe previous embodiment. The lower inner edge ill of each metal washeris rounded off in the same manneras was the lower outer edge I in theprevious embodiment.

The upper metal washer of the series fits snu ly against the metal ofthe shell to provide a good grounding connection.

Fitting snugly down upon the assemblage of washers is a conical memberI! which fits with a driving fit around the inner cigarette 2.

was formed within the lower portion 1 of the shell.

' If desired, the pile of mica washers I may be omitted as well as theupper portion of the shell, the shell being reduced in this case to thelower part 4, which merely acts as a bushing and a means of connectingthe plug to the cylinder wall 2|. I

The metal washers must resist the temperatures and gases inthe engine,but they should also possess sufliciently good heat conductivity andhave such a coefficient of expansion that upon heating of the sprak pluggood thermal contact will be maintained along the directions shown bythe arrows in Fig. 4. In other words, the metal washers should have acoefficient of expansion relative to that of the surrounding mafacturedand/or used by or for the Government of the United States of America forgovernmental The member I! fits into a correspondingly shaped repurposeswithout the payment of any royalties thereon or therefor.

We claim: 1. A spark plug assembly comprising a central spindle shank, amica sheath completely enclosing the side Walls of said shank, anoutwardly flanged head formed on the lower endof said shank, a pluralityof ring shaped terminalscarried by the lower part of said shank, aplurality of insulating disks separating said terminals and spacing themto form spark gaps between each pair of adjacent terminals, acone-shaped metal bushing fitted snugly around said mica sheath andagainst the upper one of said terminals, a metal bushing fitting snuglyover said coneshaped bushing and threaded for connecting said assemblyto the cylinder wall of an engine, a column of mica washers fittedsnugly around said sheath and down upon the upper surface of said outerbushing and meansbinding all the above mentioned'elements into a compactunit.

2. A spark plug assembly comprising a central spindle shank, a micasheath completely enclosing the side walls of said shank, an outwardlyflanged head formed on the lower end of said shank, a plurality of ringshaped terminals carried by the lower part of said shank, a plurality ofinsulating disks separating said terminals and spacing them to formspark gaps between each pair of adjacent terminals, a cone-shaped metalbushing fitted snugly around said mica sheath and against the upper oneof said terminals, a metal bushing fitting snugly over said coneshapedbushing and threaded for connecting said assembly to the cylinder wallof an engine, a column of mica washers fitted snugly around said sheathand down upon the upper surface of said outer bushing, and an outwardlyturned flange formed upon the upper endof said shank and binding all theabove mentioned elements into a compact unit.

3. A spark plug assembly comprising a cylindrical shell, a centralspindle shank extending longitudinally of said shell and terminatingshort of the lower end thereof, an insulating sheath enclosing the sidewalls of said shank, a plurality-of ring-shaped terminals contained inthe lower end of said shell and beneath said shank, a plurality ofring-shaped insulating disks interspersed between said terminals, saiddisks having larger central holes than said terminals and se ing tospace said terminals apart so that sp rk gaps are formed. between theadjacent edges of the central holes of adjacent terminals, and meansinsulating "said terminals from said shell.

4. In a spark plug, a terminal assembly comprising a plurality ofring-shaped metal terminals of generally rectangular cross section, aplurality of ring-shaped elements of insulating material, eachseparating a pair of said terminals by a distance sumcient'to create aneflicient 'spark gap between them, the diameter of the hole in each ofthe ring shaped elements being larger than that of each of thering-shaped terminals, whereby an air-gap will be formed between thecentral portion ofadjacent terminals, an insulating sheath surroundingsaid terminals and elements and'annularly'spaced from said terminals, atleast one of each pair of adjacent outer edges of each adiacent pair ofterminals being rounded off and'insulating' material filling saidannular space and means binding saidassembly together into a compactunit.

5. In a spark plug, a terminal assembly comprising a plurality ofring-shaped metal terminals oi generally rectangular cross section, aplurality ct ring-shaped elements of insulating material, eachseparating a pair of said terminals by a distance sufllcient to createan efllcient spark gap between them, the outer diameter of each oi. saidterminals beinggreater than that of said ringshaped elements, whereby anair-gap will be formed between the peripheral portions of adjacentterminals, means'passing through each of said elements and terminals andbinding the whole assembly into a compact unit, the inner diameter ofeach of said terminals being sufllcient to leave an annular spacebetween it and said binding means, at least one of each pair of adjacentinner edges of each adjacent pair of terminals being rounded off andinsulating material filling each of said spaces.

6. In a spark plug, an outer shell having a partially closed bottomformed with a central aperture, a lining of insulating material on theinside adjacent points on said adjacent terminals.

01' said shell, a terminal assembly carried therein, said assemblycomprising a plurality of ring-, shaped metal terminals, a plurality ofringshaped elements of insulating material, each separating a pair ofsaid terminals by a distance suflicient to create an efflcient spark gapbetween them, the diameter of the hole in each of the ring-shapedelements being larger than that of each of the ring-shaped terminals,whereby an air-gap will be formed between the central portions ofadjacent terminals, the outer diameter or each of said ring-shapedterminals being such' as to leave an annular space .between saidterminal and said lining, the lower outeredge of each of said terminalsbeing rounded ofl, an insulating substance filling said annular spaceand means holding said terminals and said elements into a compact unit.

7. In a spark plug, a central spindle shank, a

terminal assembly comprising a plurality 'of ring- 40 shaped terminals,a plurality oi! ring-shaped elements of insulating material, eachseparating a pair of said terminals by a distance sumcien't to create anefllcient spark gap between them, the

outer diameter of each of said terminals being i terminals and elements,a sheath of insulating material interspersed between said spindle shankand said terminals and elements, the diameter of the hole in each ofsaid terminals being such as to leave an annular space between saidsheath and said terminal, the lower inner edge of each of said terminalsbeing rounded oil, an insulating substance filling said annular space,and means comprising means on said spindle shank holding said terminalsand said elements into a compact unit.

8. A spark plug terminal, comprising a metal annulus having across-section presenting two angular outer corners and at least onerounded inner comer, said cross-section being so shaped that when aplurality of, said terminals are stacked and separated from each otherby waters of insulation, the distance between the adjacent outer cornersof adjacent terminals will be at least as short as the distance betweenany two 9. A spark plug terminal, comprising a metal annulus having across-section presenting two angular inner corners and at least onerounded outer corner, said cross-section being so shaped that when aplurality of said terminals are stacked and separated from each other bywaters of insulation, the distance between the adjacent inner corners ofadjacent terminals will be at least as short as the distance between anytwo adjacent points on said adjacent terminals.

10. A spark plug assembly comprising a central spindle shank, a'micasheath completely en- 'closing the side walls of said shank, anoutwardly flanged head formed on the lower'end 01' said shank, aplurality of ring-shaped terminals carried by the lower part of saidshank, a plurality of insulating disks separating said terminals andspacing them to form spark gaps between each pair of adjacent terminals,a cone-shaped metal bushing fitted snugly around said mica sheath abovesaid terminals, 9. metal bushing fitting snugly over said cone-shapedbushing, a column of insulation fitted snugly around said sheath anddown upon the upper surface of said outer bushing and means binding allthe above mentioned elements into a compact unit.

MELVIILE F. PETERS. HENRY K. KING.

